feat: add help for cli plugin (apple#1068)

- Closes apple#387.
- Override the swift-argument-parser `help` command
  with a version that prints the reformatted help that
  includes plugin information.

---------

Signed-off-by: ChengHao Yang <17496418+tico88612@users.noreply.github.com>

Author: tico88612

Makefile

@@ -193,6 +193,7 @@ integration: init-block
 	{ \
 		exit_code=0; \
 		CLITEST_LOG_ROOT=$(LOG_ROOT) && export CLITEST_LOG_ROOT ; \
+		$(SWIFT) test -c $(BUILD_CONFIGURATION) $(SWIFT_CONFIGURATION) --filter TestCLIHelp || exit_code=1 ; \
 		$(SWIFT) test -c $(BUILD_CONFIGURATION) $(SWIFT_CONFIGURATION) --filter TestCLIStatus || exit_code=1 ; \
 		$(SWIFT) test -c $(BUILD_CONFIGURATION) $(SWIFT_CONFIGURATION) --filter TestCLIVersion || exit_code=1 ; \
 		$(SWIFT) test -c $(BUILD_CONFIGURATION) $(SWIFT_CONFIGURATION) --filter TestCLINetwork || exit_code=1 ; \

Sources/ContainerCommands/Application.swift

@@ -45,7 +45,8 @@ public struct Application: AsyncLoggableCommand {
         abstract: "A container platform for macOS",
         version: ReleaseVersion.singleLine(appName: "container CLI"),
         subcommands: [
-            DefaultCommand.self
+            DefaultCommand.self,
+            HelpCommand.self,
         ],
         groupedSubcommands: [
             CommandGroup(
@@ -108,16 +109,15 @@ public struct Application: AsyncLoggableCommand {
         let args = Array(fullArgs.dropFirst())
 
         do {
-            // container -> defaultHelpCommand
             var command = try Application.parseAsRoot(args)
             if var asyncCommand = command as? AsyncParsableCommand {
                 try await asyncCommand.run()
             } else {
                 try command.run()
             }
         } catch {
-            // Regular ol `command` with no args will get caught by DefaultCommand. --help
-            // on the root command will land here.
+            // --help/-h on the root command (e.g. `container --help`) is intercepted
+            // by ArgumentParser and lands here.
             let containsHelp = fullArgs.contains("-h") || fullArgs.contains("--help")
             if fullArgs.count <= 2 && containsHelp {
                 let pluginLoader = try? await createPluginLoader()

Sources/ContainerCommands/HelpCommand.swift

@@ -0,0 +1,33 @@
+//===----------------------------------------------------------------------===//
+// Copyright © 2026 Apple Inc. and the container project authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//   https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//===----------------------------------------------------------------------===//
+
+import ArgumentParser
+import ContainerAPIClient
+
+struct HelpCommand: AsyncLoggableCommand {
+    public static let configuration = CommandConfiguration(
+        commandName: "help",
+        shouldDisplay: false
+    )
+
+    @OptionGroup(visibility: .hidden)
+    public var logOptions: Flags.Logging
+
+    func run() async throws {
+        let pluginLoader = try? await Application.createPluginLoader()
+        await Application.printModifiedHelpText(pluginLoader: pluginLoader)
+    }
+}

Tests/CLITests/TestCLIHelp.swift

@@ -0,0 +1,39 @@
+//===----------------------------------------------------------------------===//
+// Copyright © 2026 Apple Inc. and the container project authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//   https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//===----------------------------------------------------------------------===//
+
+import Foundation
+import Testing
+
+class TestCLIHelp: CLITest {
+    @Test func testHelp() throws {
+        let (_, output, error, status) = try run(arguments: ["help"])
+        #expect(status == 0, "help should succeed, stderr: \(error)")
+
+        #expect(
+            output.contains("OVERVIEW: A container platform for macOS"),
+            "output should contain overview section"
+        )
+    }
+    @Test func testDebugHelp() throws {
+        let (_, output, error, status) = try run(arguments: ["--debug", "help"])
+        #expect(status == 0, "help should succeed, stderr: \(error)")
+
+        #expect(
+            output.contains("OVERVIEW: A container platform for macOS"),
+            "output should contain overview section"
+        )
+    }
+}